2.1. Respiratory Syncytial Virus in Disease
RS virus is a major cause of lower respiratory disease in infancy and early childhood (McIntosh and Chanock, 1985, in Virology, Fields, B. (ed), Raven, NY, pp. 1285-1304). In all geographical areas, it is the major cause of bronchiolitis and pneumonia in infants and young children. The agent reinfects frequently during childhood, but illness produced by reinfection is generally milder than that associated with the initial infection and rarely causes major problems.
RS virus is an enveloped RNA virus of the family Paramyxoviridae and of the genus pneumovirus. The two major envelope proteins are the G protein, which is responsible for attachment of the virus to the host cell membrane, and the fusion protein, which is responsible for fusing the virus and cell membranes. Virus-cell fusion is a necessary step for infection. Fusion protein is also required for cell-cell fusion which is another way to spread the infection from an infected cell to an uninfected cell.
Antibodies directed against the fusion protein or against the G protein can neutralize the virus. However, only antibodies to the fusion protein will block the spread of the virus between cells, i.e. have anti-fusion activity. Thus, antibodies to the fusion protein will protect against circulating virus as well as inhibit the spread, between cells, of an established infection. Antibodies to the fusion protein (both polyclonal antisera against purified fusion protein and monoclonal antibodies which contain both neutralizing and anti-fusion activity) have been found to be protective in animal models against infection (Walsh et al., 1984, Infect. Immun. 43:756-758).